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<h1><a href="https://archiveofourown.org/works/23433451">Cycle</a> by <a class='authorlink' href='https://archiveofourown.org/users/MercuryGray/pseuds/MercuryGray'>MercuryGray</a></h1>

<table class="full">

<tr><td><b>Category:</b></td><td>Dunkirk (2017)</td></tr>

<tr><td><b>Genre:</b></td><td>Bletchley Park, Character Study, Cryptography, Future Fic, Gen, Mathematicians, Originally Posted on Tumblr, Tumblr Prompt</td></tr>

<tr><td><b>Language:</b></td><td>English</td></tr>

<tr><td><b>Status:</b></td><td>Completed</td></tr>

<tr><td><b>Published:</b></td><td>2020-04-01</td></tr>

<tr><td><b>Updated:</b></td><td>2020-04-01</td></tr>

<tr><td><b>Packaged:</b></td><td>2021-05-01 11:07:26</td></tr>

<tr><td><b>Rating:</b></td><td>Not Rated</td></tr>

<tr><td><b>Warnings:</b></td><td>No Archive Warnings Apply</td></tr>

<tr><td><b>Chapters:</b></td><td>1</td></tr>

<tr><td><b>Words:</b></td><td>631</td></tr>

<tr><td><b>Publisher:</b></td><td>archiveofourown.org</td></tr>

<tr><td><b>Story URL:</b></td><td>https://archiveofourown.org/works/23433451</td></tr>

<tr><td><b>Author URL:</b></td><td>https://archiveofourown.org/users/MercuryGray/pseuds/MercuryGray</td></tr>

<tr><td><b>Summary:</b></td><td><div class="userstuff">
              <p>
  <i>The machine itself was a problem waiting to be solved, but there was a sanctity in the numbers. The machine was clever, but numbers did not lie.</i>
</p><p> </p><p>Peter's contribution to the war effort will be different than his brother's.</p>
            </div></td></tr>

<tr><td><b>Comments:</b></td><td>4</td></tr>

<tr><td><b>Kudos:</b></td><td>5</td></tr>

</table>

<a name="section0001"><h2>Cycle</h2></a>
<div class="story"><div class="fff_chapter_notes fff_head_notes"><b>Author's Note:</b><blockquote class="userstuff">
      <p>Done for a prompt on tumblr: one character + one word, Peter Dawson + cycle</p><p>cy·cle | \ ˈsī-kəl  \ an interval of time during which a sequence of a recurring succession of events or phenomena is completed;  a permutation of a set of ordered elements in which each element takes the place of the next and the last becomes first ; a takeoff and landing of an airplane</p>
    </blockquote></div><div class="userstuff module">
    
    <p>Twenty-six letters in the alphabet, four rotors to a machine. Four hundred forty-nine thousand four hundred permutations, accounting for the ratchets and keys that ensured no letter would fall on itself. 16.93 percent of letters expected to be E, 10.53 percent of letters expected to be N, 8.02 percent of letters expected to be I.</p><p>The machine itself was a problem waiting to be solved, but there was a sanctity in the numbers. The machine was clever, but numbers did not lie.</p><p>From his earliest years Peter had found comfort in sums and totals, a great serenity in the mathematics of the universe. There were cycles and repetitions in everything, if one only stopped to look hard enough. He could not remember a time when this had not been so; his father let him do his sums at the kitchen table alongside his brother, helping the two boys through their long division and their algebra, and then pulling out his ancient navigation textbooks and walking them through their sines and cosines and the use of logarithmics to find their bearings out at sea. Was it the numbers that brought him solace, or the time spent with his father? Peter never knew. Mathematics seemed to other boys a foreign country, where they spoke a different language, but he approached it as he would his homeland, a place where his voice was always understood.</p><p>Four points on a compass, three hundred and sixty degrees in a full turn, one hundred and eighty degrees east and west, ninety degrees north and south  - but always one north star, one direction home. David would complain when they took bearings and headings and their father made them do the math to determine latitudes and longitudes, but who was it who came in first in his navigation class, leaving the rest of the pilots behind? When he came home he and Peter took the Moonstone out one afternoon so they could talk freely. “It’s like nothing in the world, Pete,” his brother would say of flying. “It’s like …someone bottled happiness.”</p><p>Peter kept his hands on the wheel and thought of plotting tables and adding machines. He’d be twenty next year - old enough to volunteer, certainly. But he didn’t see himself as a soldier, or a pilot. A sailor, maybe, if the Navy would take him. The sea had patterns, tides. Navigation was mathematics. But then David’s plane was shot down, and the world shifted, and Peter put away the application for the Navy - until the Navy came and found him. Stern looking men in blue, with gold braid on their cuffs.</p><p><em>They’ve come about Dunkirk</em>, he thought to himself. <em>They’ve come about Dad.</em></p><p>But they hadn’t come for Amos Dawson - they’d come for Peter. They produced copies of his school certificates, let him run through a few proofs. And, after he’d signed the official secrets act, they introduced him to the Machine. Twenty-six letters on a rotor, four rotors to a set, five plugs on the board, a code that changed every day in random motion.  A problem, a puzzle. An Enigma. Each transmission had a pattern to it, a greeting, an ending. If you could solve those things you learned more about the machine, how it moved, how it thought.</p><p>And if they learned the machine, the letters became words, and the words became intelligence, and intelligence meant that resources were not wasted, that decisions could be made, that bombs would land on target.</p><p>That pilots would come home.</p><p>Under his pencil the words took shape, and as soon as the first message of the day had gone to the translators, Peter returned to his crib and began again, twenty six letters, four rotors, five pegs, a cycle that never seemed to end.</p>
  </div><div class="fff_chapter_notes fff_foot_notes"><b>Author's Note:</b><blockquote class="userstuff"><p>As Peter is a sailor, I decided making him good at math wasn't too far of a stretch. The Government Code and Cipher School (GCCS) at Bletchley recruited all kinds of people to break codes, even going so far as to put a call out for people who were good at crossword puzzles. I'm afraid I haven't done a super-good job explaining how an Enigma machine works, but to be fair, they're really, really complicated.</p><p>If you're looking for a good look general look at code breaking, The Secret Lives of Codebreakers, by Sinclair McKay, was very good.  I also enjoyed The Debs of Bletchley Park, which focused specifically on the upper class women who were recruited to assist in code-breaking.</p></blockquote></div></div>
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